Le Bret is Cyrano’s closest friend, his fellow Cadet, and a voice of reason to our less practical hero. Cyrano trusts Le Bret enough to confide in him and reveal his secrets. Le Bret responds by trying to be a peacemaker; unfortunately, Cyrano rarely listens.
Observant and shrewd, Le Bret is the character to guess the object of Cyrano’s affections and pinpoint how many enemies the man has made. His honest questions often trigger Cyrano’s lengthy soliloquies in which he explains his morals.
Le Bret is probably the character with whom readers can most easily identify. He sees the Cyrano-Christian-Roxane love triangle with an objective eye and often tells Cyrano when he is being foolish. He has Cyrano’s ear, listens to him, and advises him as most reasonable readers probably would. That he is rarely heeded is a reflection both of Cyrano’s romanticism and of the play’s fantastical world.
But perhaps Le Bret’s most important role in the play is to give us information on Cyrano that we would not otherwise know, especially in the first act and before we actually meet the story’s hero. See "Character Role Identification" for more, as this is a pretty standard tool in classic literature.
Lastly, we thought you should know that the historical Le Bret was indeed a close friend of Cyrano’s and wrote a biography on him; thus it comes as no surprise that the literary Le Bret should know so much about the fictional de Bergerac.